There’s an interesting paper on millicents (digital cash worth about a thousandth of a cent) from a guy who seems to be involved in Microsoft’s Penny Black project.
A decade hence, assuming that computers (and their components) continue on the price and performance curves of the last two decades, the minimum transaction grain will be an order of magnitude smaller than it is today. The smallest transactions will be in the sub-penny range. In a decade, we will see pricing by the web page. We can unbundle the newspaper and the magazine, derive revenue from the newspaper morgue, and sell information without restricting consumers to a subscription to a small number of sources.
Interesting thought experiment: imagine an average fee of about .1c/MB ($1/GB) integrated into http. You can probably setup a browser to obey this, so that it just displays “this image too expensive, right click to download anyway” when appropiate. It’s no more expensive than traditional bandwidth charges (10c/MB in Australia), and it sets up an economy so that when you’re slashdotted for writing something way cool you have a chance at making a profit instead of a loss. It potentially gives you a way of rate-limiting users too if you’re overloaded — just raise the prices until you’re not. The numbers might not work out, but in theory should do. Search engines might have problems — they need to scour the web, which would potentially cost a lot of money; but either it already does that, or it’s already subsidised elsewhere, and they already get a bunch of hits. Still, a market should be able to cope with this, possibly by making google.com marginally more expensive to view than other sites.
Note that this doesn’t quite match the email scheme — it presumes downloaders stop paying their ISP per MB, and pay the websites they view instead. Which means the websites pay their ISPs instead, which means fees can be based on outgoing traffic instead of incoming traffic, which in turn puts the burden of paying for the traffic of slammer worms and the like where it belongs. I may be drawing to long a bow at this point.
I’m obsessed with market theory :(
If this theory pans out, then you could make a good argument for allocating the entire social cost of spam to David Chaum’s patent on ecash.